Investigation of commercial sodium cacodylate trihydrate: penta-[mu]-aqua-disodium(I) bis­(dimethyl­arsenate) and di-[mu]-aqua-bis­[triaqua­sodium(I)] bis­(dimethyl­arsenate)

Crystals from commercial samples of sodium cacodylate trihydrate, NaO₂As(CH₃)₂·3H₂O, were analyzed by single-crystal X-ray diffraction and two phases were identified, viz. penta-[mu]-aqua-disodium(I) bis­(dimethyl­arsenate), {[Na₂(H₂O)₅](C₂H₆AsO₂)₂}_n, (I), and di-[mu]-aqua-bis­[triaqua­sodium(I)] bis­(dimethyl­arsenate), [Na₂(H₂O)₈](C₂H₆AsO₂)₂, (II). Both (I) and (II) form layered structures in which hydrated Na⁺ ions form layers in the ab plane, the cacodylate ions being located in between the layers. In (I), the two non-equivalent Na⁺ ions (located at twofold axes) and the three non-equivalent aqua ligands (one of which also lies on a twofold axis) form infinite polymeric layers, but in (II), layers of discrete centrosymmetric [Na₂(H₂O)₈]²⁺ ions are present. One of the commercial samples analyzed contained almost exclusively crystals of the tetra­hydrate (II), while another sample consisted of a mixture of the two phases.

S1. Comment

The first salts of cacodylic acid were prepared by Robert Bunsen in 1842 during his famous studies on the cacodyl radical in 1837–1843 (Bunsen, 1891). Bunsen informed Berzelius, who wrote an account for the results in his annual report on the progress of chemistry for 1842 (Berzelius, 1842), which is the first publication on the subject. Although more than 160 years have passed, none of the salts are found in the Cambridge Structural Database (CSD; Version 5.28 of November 2006; Allen 2002). Sodium cacodylate trihydrate is today commercially available; one important use is in buffer solutions which find use in protein crystallization (Ericsson et al., 2006; Izaac et al., 2006). Examination of a commercial sample showed that it contained crystals of two distinct morphologies, mainly round irregularly shaped crystals (some of which displayed well developed faces), but also a few crystal plates. It was possible to select crystals suitable for single-crystal X-ray diffraction, and the plates were identified as the expected trihydrate, [{Na(H₂O)₃}_∞]{O₂As(CH₃)₂}_∞, (I), but the irregular crystals were identified as a tetrahydrate, [Na₂(H₂O)₈]{O₂As(CH₃)₂}₂, (II). Another commercial sample was shown by powder X-ray diffraction to consist almost exclusively of the tetrahydrate, (II). The weight loss on drying this sample at 433 K overnight is also consistent with the expected weight loss on dehydratization of the tetrahydrate. A tetrahydrate of sodium cacodylate does not appear to be officially available on a commercial basis. SciFinder Scholar 2006 (American Chemical Society, 2005) lists 29 commercial sources for sodium cacodylate; of these, 11 are given simply as `sodium cacodylate' and may be the anhydrous product, 6 are given as `sodium cacodylate hydrate' and 12 as the trihydrate. Care should be taken on using sodium cacodylate, when molar mass is a matter of importance.

There are two non-equivalent Na ions in the structure of (I), Na1 and Na2, both located on twofold axes (Fig. 1). All of the three water molecules in (I) are coordinated to Na ions and give rise to infinite layers in the ab plane. Both Na1 and Na2 are five-coordinate, with coordination geometries intermediate between trigonal–bipyramidal and square-pyramidal. The coordination geometry around atom Na1 is perhaps closer to square-pyramidal, while Na2 is perhaps closer to trigonal–bipyramidal coordination geometry. The aqua ligands are bridging between atoms Na1 and Na2. Atom O5 forms a single bridge between atoms Na1 and Na2; atoms O3 and O3(x, y, 1/2 - z) form two bridges between atoms Na2 and Na1(1 - x, -1/2 + y, 1/2 - z); and atoms O4 and O4(x, y, 1/2 - z) form two bridges between atoms Na2 and Na1(1 + x, y, z). The resulting layer is depicted in Fig. 2. The cacodylate anions are located in between the Na/H₂O layers and form hydrogen bonds to the layers. Atom O2 interacts with atoms H3, H5 and H7(1 - x, -1/2 + y, z); atom O1 interacts with atoms H4(-1 + x, y, z) and H6(-1 + x, y, z). All of these H atoms are in the same layer. There are no directed attractive forces between the anions; one reason is that only relatively weak C—H···O interactions could form. The geometry of the cacodylate anion is unremarkable, with only a slight degree of distortion from ideal tetrahedral coordination geometry around the central As atom.

In the crystal structure of (II), the Na⁺ ions and water molecules give rise to discrete dinuclear cations (Fig. 3) rather than the infinite layers present in (I). As in (I), atom Na1 is five-coordinate and the coordination geometry is best described as trigonal–bipyramidal, distorted towards square-pyramidal geometry. Atoms Na1 and Na1^vii [symmetry code: (vii) 1/2 - x, 3/2 - y, 1 - z] are linked by two µ₂-aqua ligands corresponding to atoms O5 and O5^vii. One of the two bridging aqua ligands is in an equatorial position and the other is in an axial position in the coordination environment of atom Na1. The resulting bis(µ₂-aqua)(hexaaqua)disodium ion appears to be very rare in combination with organic counter-ions; there is only one further example in the CSD (Laborda et al., 2004). A number of similar ions are, however, found in the CSD, where the Na atoms are six-coordinate.

As in the structure of (I), the crystal structure of (II) is built up by layers of Na⁺ ions and water molecules in the ab plane {although in the form of discrete [Na₂(H₂O)₈]²⁺ ions}, with the anions appearing between the layers, the components being linked by hydrogen bonds. Within the asymmetric unit, there is one short contact between the anion and the cation (O1—H3A; Table 3). In addition, atom O1 forms two short intermolecular contacts, to H3B(-x, y, 1/2 - z) and H6A(1/2 - x, -1/2 + y, 1/2 - z), and atom O2 forms four short intermolecular contacts, to H5B(-1/2 + x, 3/2 - y, -1/2 + z), H4B(1/2 - x, -1/2 + y, 1/2 - z), H5A(1/2 - x, 1/2 + y, 1/2 - z) and H4A(x, 2 - y, -1/2 + z) (Table 3). The cation forms four equivalent short contacts (2.10 Å), beside those involving O1 and O2: O4···H6b^viii [symmetry code: (viii) 1 - x, 2 - y, 1 - z], H6b–O4^viii, O4^vii–H6b^ix [symmetry code: (ix) -1/2 + x, -1/2 + y, z], and O4^ix–H6B^vii. The crystal structure of (II) is depicted in Fig. 4 (along the a axis) and in Fig. 5 (along the b axis). The formation of layers in the ab plane is most easily seen from Fig. 4.

Related literature

For related literature, see: Allen (2002); American (2005); Berzelius (1842); Bunsen (1891); Ericsson et al. (2006); Izaac et al. (2006); Laborda et al. (2004).

S2. Experimental

Crystals were carefully selected from a commercial sample of `sodium cacodylate trihydrate'.

S3. Refinement

All H-atom parameters were refined without constraints, except for the U_iso(H) values in (I), which were set to 1.2U_eq(C) and 1.5U_eq(O). [Please check.]

Computing details

For both compounds, data collection: CrystalClear (Rigaku, 2000); cell refinement: CrystalClear (Rigaku, 2000); data reduction: CrystalClear (Rigaku, 2000); program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997) and PLATON (Spek, 2003); software used to prepare material for publication: SHELXL97 (Sheldrick, 1997).

Figures

	Fig. 1. The structure of (I) showing crystallographic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. All H atoms have been omitted.
	Fig. 2. Na^+ ions and water molecules form infinite layers in (I). The layer is viewed along the c axis. The appearance of double µ2-bridges in the structure cannot be seen in the figure, since the water molecules giving rise to them are superimposed. The cacodylate ions have been omitted.
	Fig. 3. The structure of (II), showing the crystallographic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. All H atoms have been omitted.
	Fig. 4. The unit cell of (II), viewed along the a-axis direction. All H atoms have been omitted. Three layers run vertically in the figure. Layers of hydrated sodium ions are separated by cacodylate ions.
	Fig. 5. The unit cell of (II), viewed along the b-axis direction. All H atomshave been omitted. Three layers of bis(µ2-aqua)(hexaaqua)disodium ions runs vertically in the figure, the layers being separated by cacodylate ions.

(I) penta-µ-aqua-disodium(I) bis(dimethylarsenate)

Crystal data

[Na2(H2O)5](C2H6AsO2)2	F(000) = 824
Mr = 410.04	Dx = 1.729 Mg m^−3
Orthorhombic, Pbcm	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2c 2b	Cell parameters from 1585 reflections
a = 6.1299 (11) Å	θ = 1.7–26.0°
b = 10.7515 (18) Å	µ = 4.32 mm^−1
c = 23.901 (4) Å	T = 100 K
V = 1575.2 (5) Å^3	Irregular, colourless
Z = 4	0.3 × 0.2 × 0.2 mm

Data collection

Rigaku R-AXIS IIC image-plate system diffractometer	1585 independent reflections
Radiation source: rotating-anode X-ray tube, Rigaku H3R	1493 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.052
Detector resolution: 105 pixels mm^-1	θmax = 26.0°, θmin = 1.7°
ϕ scans	h = −7→7
Absorption correction: multi-scan (CrystalClear; Rigaku, 2000)	k = −12→13
Tmin = 0.255, Tmax = 0.420	l = −29→29
10364 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.033	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.067	Only H-atom coordinates refined
S = 1.18	w = 1/[σ^2(Fo^2) + (0.0289P)^2 + 1.7086P] where P = (Fo^2 + 2Fc^2)/3
1585 reflections	(Δ/σ)max < 0.001
115 parameters	Δρmax = 0.40 e Å^−3
0 restraints	Δρmin = −0.45 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
C1	0.3585 (6)	0.1594 (3)	0.41682 (14)	0.0186 (6)
C2	0.2396 (5)	−0.1048 (3)	0.46167 (13)	0.0192 (6)
As1	0.18837 (4)	0.01275 (2)	0.402786 (10)	0.00707 (11)
Na1	0.1353 (2)	0.28419 (13)	0.2500	0.0098 (3)
Na2	0.6967 (2)	0.09170 (14)	0.2500	0.0107 (3)
O1	−0.0764 (3)	0.04993 (18)	0.40040 (8)	0.0121 (4)
O2	0.2782 (3)	−0.05114 (17)	0.34272 (8)	0.0101 (4)
O3	0.7111 (3)	−0.07794 (18)	0.31658 (9)	0.0118 (4)
O4	0.8610 (3)	0.2188 (2)	0.31589 (8)	0.0121 (4)
O5	0.3110 (5)	0.0934 (3)	0.2500	0.0119 (6)
H1A	0.316 (5)	0.191 (3)	0.4522 (15)	0.014*
H1B	0.497 (6)	0.137 (3)	0.4179 (13)	0.014*
H1C	0.328 (5)	0.220 (3)	0.3867 (15)	0.014*
H2A	0.189 (5)	−0.073 (3)	0.4958 (15)	0.014*
H2B	0.387 (6)	−0.121 (3)	0.4636 (14)	0.014*
H2C	0.163 (5)	−0.182 (3)	0.4541 (14)	0.014*
H3	0.579 (6)	−0.077 (3)	0.3245 (14)	0.018*
H4	0.778 (6)	−0.049 (4)	0.3397 (16)	0.018*
H5	0.285 (5)	0.048 (3)	0.2786 (14)	0.018*
H6	0.884 (6)	0.168 (3)	0.3473 (15)	0.018*
H7	0.819 (6)	0.279 (4)	0.3260 (16)	0.018*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0211 (15)	0.0168 (15)	0.0179 (15)	−0.0023 (12)	−0.0043 (13)	−0.0054 (12)
C2	0.0246 (17)	0.0204 (15)	0.0126 (14)	0.0107 (13)	0.0033 (13)	0.0053 (12)
As1	0.00877 (16)	0.00727 (16)	0.00517 (16)	0.00090 (9)	−0.00079 (10)	−0.00025 (10)
Na1	0.0097 (7)	0.0086 (7)	0.0109 (8)	−0.0008 (5)	0.000	0.000
Na2	0.0139 (8)	0.0083 (7)	0.0098 (7)	−0.0011 (6)	0.000	0.000
O1	0.0106 (9)	0.0162 (10)	0.0095 (9)	0.0040 (8)	−0.0006 (8)	−0.0009 (7)
O2	0.0121 (9)	0.0097 (9)	0.0086 (9)	0.0002 (8)	0.0015 (8)	−0.0015 (7)
O3	0.0087 (9)	0.0153 (10)	0.0113 (10)	0.0010 (8)	−0.0007 (8)	−0.0022 (8)
O4	0.0177 (10)	0.0078 (10)	0.0109 (10)	0.0010 (8)	0.0005 (8)	−0.0025 (8)
O5	0.0170 (15)	0.0110 (14)	0.0076 (13)	0.0004 (11)	0.000	0.000

Geometric parameters (Å, º)

C1—As1	1.920 (3)	Na1—Na2	4.016 (2)
C1—H1A	0.95 (4)	Na2—O4	2.316 (2)
C1—H1B	0.88 (4)	Na2—O5	2.364 (3)
C1—H1C	0.99 (3)	Na2—O3	2.422 (2)
C2—As1	1.918 (3)	Na2—Na1^iv	3.393 (2)
C2—H2A	0.94 (4)	Na2—Na1^v	3.463 (2)
C2—H2B	0.92 (3)	Na2—H3	2.64 (3)
C2—H2C	0.97 (3)	Na2—H4	2.67 (4)
As1—O1	1.6725 (19)	Na2—H5	2.66 (3)
As1—O2	1.6840 (18)	O3—H3	0.83 (4)
Na1—O5	2.317 (3)	O3—H4	0.75 (4)
Na1—O3^i	2.370 (2)	O4—H6	0.94 (4)
Na1—O4^ii	2.409 (2)	O4—H7	0.74 (4)
Na1—Na2^ii	3.393 (2)	O5—H5	0.86 (3)
Na1—Na2^iii	3.463 (2)
As1—C1—H1A	108 (2)	Na1^iv—Na2—Na1^v	110.28 (4)
As1—C1—H1B	108 (2)	O4—Na2—Na1	93.93 (7)
H1A—C1—H1B	109 (3)	O5—Na2—Na1	30.59 (7)
As1—C1—H1C	108.0 (19)	O3—Na2—Na1	114.80 (6)
H1A—C1—H1C	111 (3)	Na1^iv—Na2—Na1	111.39 (5)
H1B—C1—H1C	113 (3)	Na1^v—Na2—Na1	138.33 (5)
As1—C2—H2A	110 (2)	O4—Na2—H3	93.7 (7)
As1—C2—H2B	109 (2)	O4^vii—Na2—H3	169.2 (8)
H2A—C2—H2B	110 (3)	O5—Na2—H3	74.5 (8)
As1—C2—H2C	110 (2)	O3^vii—Na2—H3	86.4 (7)
H2A—C2—H2C	108 (3)	O3—Na2—H3	18.2 (8)
H2B—C2—H2C	109 (3)	Na1^iv—Na2—H3	129.4 (7)
O1—As1—O2	112.69 (9)	Na1^v—Na2—H3	55.0 (8)
O1—As1—C2	109.97 (12)	Na1—Na2—H3	96.9 (8)
O2—As1—C2	107.66 (11)	O4—Na2—H4	73.0 (9)
O1—As1—C1	109.67 (12)	O4^vii—Na2—H4	143.1 (8)
O2—As1—C1	107.84 (12)	O5—Na2—H4	101.0 (8)
C2—As1—C1	108.91 (15)	O3^vii—Na2—H4	95.4 (9)
O5—Na1—O3^i	111.66 (9)	O3—Na2—H4	16.1 (8)
O3^iii—Na1—O3^i	84.37 (11)	Na1^iv—Na2—H4	101.4 (8)
O5—Na1—O4^ii	93.80 (9)	Na1^v—Na2—H4	53.4 (8)
O3^iii—Na1—O4^ii	91.19 (7)	Na1—Na2—H4	116.8 (7)
O3^i—Na1—O4^ii	154.01 (10)	H3—Na2—H4	28.4 (10)
O4^vi—Na1—O4^ii	81.67 (11)	O4—Na2—H5	110.0 (7)
O5—Na1—Na2^ii	80.12 (8)	O4^vii—Na2—H5	133.9 (8)
O3^iii—Na1—Na2^ii	134.13 (6)	O5—Na2—H5	18.5 (7)
O4^vi—Na1—Na2^ii	43.02 (5)	O3^vii—Na2—H5	94.0 (8)
O5—Na1—Na2^iii	134.99 (9)	O3—Na2—H5	74.4 (8)
O3^iii—Na1—Na2^iii	44.33 (5)	Na1^iv—Na2—H5	149.4 (8)
O4^ii—Na1—Na2^iii	119.09 (7)	Na1^v—Na2—H5	96.5 (8)
Na2^ii—Na1—Na2^iii	144.89 (5)	Na1—Na2—H5	43.8 (8)
O5—Na1—Na2	31.27 (8)	H3—Na2—H5	56.3 (11)
O3^i—Na1—Na2	88.97 (7)	H4—Na2—H5	82.5 (11)
O4^ii—Na1—Na2	116.61 (7)	Na1^v—O3—Na2	92.54 (8)
Na2^ii—Na1—Na2	111.39 (5)	Na1^v—O3—H3	123 (2)
Na2^iii—Na1—Na2	103.72 (4)	Na2—O3—H3	96 (2)
O4—Na2—O4^vii	85.70 (11)	Na1^v—O3—H4	122 (3)
O4—Na2—O5	115.49 (8)	Na2—O3—H4	101 (3)
O4—Na2—O3^vii	151.08 (10)	H3—O3—H4	111 (3)
O4—Na2—O3	88.95 (7)	Na2—O4—Na1^iv	91.78 (8)
O4^vii—Na2—O3	151.08 (10)	Na2—O4—H6	105 (2)
O5—Na2—O3	92.43 (8)	Na1^iv—O4—H6	126 (2)
O3^vii—Na2—O3	82.15 (11)	Na2—O4—H7	126 (3)
O4—Na2—Na1^iv	45.20 (6)	Na1^iv—O4—H7	102 (3)
O5—Na2—Na1^iv	141.98 (9)	H6—O4—H7	108 (4)
O3—Na2—Na1^iv	115.48 (7)	Na1—O5—Na2	118.14 (13)
O4—Na2—Na1^v	115.73 (7)	Na1—O5—H5	115 (2)
O5—Na2—Na1^v	107.74 (9)	Na2—O5—H5	100 (2)
O3—Na2—Na1^v	43.13 (5)

Symmetry codes: (i) −x+1, y+1/2, −z+1/2; (ii) x−1, y, z; (iii) −x+1, y+1/2, z; (iv) x+1, y, z; (v) −x+1, y−1/2, z; (vi) x−1, y, −z+1/2; (vii) x, y, −z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H3···O2	0.83 (4)	1.917	2.742 (3)	172.69
O3—H4···O1^iv	0.75 (4)	2.010	2.757 (3)	171.36
O5—H5···O2	0.86 (3)	1.865	2.714 (3)	170.58
O4—H6···O1^iv	0.94 (4)	1.809	2.743 (3)	171.46
O4—H7···O2^iii	0.74 (4)	1.964	2.693 (3)	171.73

Symmetry codes: (iii) −x+1, y+1/2, z; (iv) x+1, y, z.

(II) di-µ-aqua-bis[triaquasodium(I)] bis(dimethylarsenate)

Crystal data

[Na2(H2O)8](C2H6AsO2)2	F(000) = 944
Mr = 464.08	Dx = 1.640 Mg m^−3
Monoclinic, C2/c	Melting point: not measured K
Hall symbol: -C 2yc	Mo Kα radiation, λ = 0.71073 Å
a = 11.516 (3) Å	Cell parameters from 5714 reflections
b = 8.838 (2) Å	θ = 2.2–25.5°
c = 19.635 (5) Å	µ = 3.65 mm^−1
β = 109.907 (8)°	T = 303 K
V = 1879.1 (8) Å^3	Block, colourless
Z = 4	0.25 × 0.15 × 0.10 mm

Data collection

Rigaku R-AXIS IIc image-plate system diffractometer	1652 independent reflections
Radiation source: rotating-anode X-ray tube, Rigaku RU-H3R	1517 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.032
Detector resolution: 105 pixels mm^-1	θmax = 25.5°, θmin = 2.2°
ϕ scans	h = −13→13
Absorption correction: multi-scan (CrystalClear; Rigaku, 2000)	k = −10→10
Tmin = 0.373, Tmax = 0.696	l = −23→23
5714 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.018	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.044	All H-atom parameters refined
S = 1.00	w = 1/[σ^2(Fo^2) + (0.0278P)^2] where P = (Fo^2 + 2Fc^2)/3
1652 reflections	(Δ/σ)max = 0.001
125 parameters	Δρmax = 0.28 e Å^−3
0 restraints	Δρmin = −0.20 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
C1	0.1060 (2)	1.04565 (19)	0.17722 (11)	0.0425 (4)
H1A	0.1371	1.1313	0.1588	0.064*
H1B	0.1294	1.0538	0.2289	0.064*
H1C	0.0176	1.0430	0.1561	0.064*
C2	0.34923 (17)	0.8666 (2)	0.19694 (11)	0.0383 (4)
H2A	0.3817	0.9539	0.1805	0.057*
H2B	0.3832	0.7767	0.1837	0.057*
H2C	0.3711	0.8706	0.2487	0.057*
O1	0.11507 (11)	0.71695 (12)	0.18493 (6)	0.0275 (2)
O2	0.13842 (10)	0.85626 (10)	0.06215 (6)	0.0243 (2)
O3	0.13255 (14)	0.76248 (17)	0.33138 (8)	0.0424 (3)
O4	0.33169 (13)	1.08614 (14)	0.50682 (8)	0.0355 (3)
O5	0.37936 (13)	0.64835 (14)	0.50201 (7)	0.0277 (3)
O6	0.41984 (15)	0.94080 (17)	0.38455 (9)	0.0394 (3)
Na1	0.27390 (6)	0.86194 (6)	0.43443 (4)	0.02757 (16)
As1	0.173618 (13)	0.863667 (15)	0.153124 (7)	0.01910 (8)
H3A	0.137 (2)	0.746 (3)	0.2950 (14)	0.055 (8)*
H3B	0.068 (3)	0.753 (3)	0.3327 (13)	0.055 (8)*
H4A	0.276 (3)	1.109 (3)	0.5193 (16)	0.058 (8)*
H4B	0.342 (2)	1.162 (3)	0.4851 (15)	0.060 (8)*
H5A	0.371 (2)	0.570 (3)	0.4824 (12)	0.038 (6)*
H5B	0.449 (2)	0.658 (2)	0.5194 (13)	0.037 (6)*
H6A	0.411 (2)	1.013 (3)	0.3684 (13)	0.043 (7)*
H6B	0.492 (3)	0.940 (3)	0.4146 (16)	0.068 (8)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0568 (12)	0.0292 (8)	0.0532 (11)	0.0011 (8)	0.0339 (10)	−0.0085 (8)
C2	0.0247 (9)	0.0536 (12)	0.0328 (9)	−0.0058 (7)	0.0049 (7)	0.0064 (7)
O1	0.0321 (6)	0.0273 (5)	0.0286 (6)	−0.0053 (5)	0.0173 (5)	−0.0002 (4)
O2	0.0264 (6)	0.0286 (6)	0.0187 (5)	0.0019 (4)	0.0087 (5)	0.0001 (4)
O3	0.0286 (8)	0.0722 (10)	0.0284 (7)	−0.0055 (6)	0.0124 (6)	−0.0105 (6)
O4	0.0425 (8)	0.0281 (6)	0.0454 (7)	0.0008 (6)	0.0273 (6)	0.0016 (6)
O5	0.0216 (7)	0.0292 (7)	0.0309 (6)	0.0001 (5)	0.0072 (5)	−0.0046 (5)
O6	0.0408 (9)	0.0373 (8)	0.0465 (8)	0.0009 (6)	0.0234 (7)	0.0092 (7)
Na1	0.0288 (4)	0.0281 (3)	0.0274 (3)	0.0001 (2)	0.0116 (3)	0.0005 (2)
As1	0.01939 (11)	0.02204 (11)	0.01779 (11)	−0.00102 (5)	0.00883 (7)	−0.00146 (5)

Geometric parameters (Å, º)

C1—As1	1.9152 (17)	O3—H3A	0.75 (3)
C1—H1A	0.9600	O3—H3B	0.75 (3)
C1—H1B	0.9600	O4—Na1	2.3969 (15)
C1—H1C	0.9600	O4—H4A	0.78 (3)
C2—As1	1.9095 (19)	O4—H4B	0.82 (3)
C2—H2A	0.9600	O5—Na1	2.3878 (14)
C2—H2B	0.9600	O5—H5A	0.78 (2)
C2—H2C	0.9600	O5—H5B	0.76 (2)
O1—As1	1.6771 (10)	O6—Na1	2.3218 (15)
O2—As1	1.6931 (12)	O6—H6A	0.71 (2)
O3—Na1	2.2965 (16)	O6—H6B	0.84 (3)
As1—C1—H1A	109.5	Na1—O6—H6A	116.2 (19)
As1—C1—H1B	109.5	Na1—O6—H6B	112.8 (19)
H1A—C1—H1B	109.5	H6A—O6—H6B	107 (3)
As1—C1—H1C	109.5	O3—Na1—O6	98.10 (7)
H1A—C1—H1C	109.5	O3—Na1—O5	105.12 (6)
H1B—C1—H1C	109.5	O6—Na1—O5	99.64 (6)
As1—C2—H2A	109.5	O3—Na1—O4	144.03 (6)
As1—C2—H2B	109.5	O6—Na1—O4	84.68 (6)
H2A—C2—H2B	109.5	O5—Na1—O4	109.75 (6)
As1—C2—H2C	109.5	O3—Na1—O5^i	90.97 (6)
H2A—C2—H2C	109.5	O6—Na1—O5^i	164.22 (5)
H2B—C2—H2C	109.5	O5—Na1—O5^i	90.34 (5)
Na1—O3—H3A	131 (2)	O4—Na1—O5^i	80.43 (5)
Na1—O3—H3B	115.0 (19)	O3—Na1—Na1^i	101.16 (5)
H3A—O3—H3B	114 (3)	O6—Na1—Na1^i	144.33 (6)
Na1—O4—H4A	108.0 (18)	O5—Na1—Na1^i	46.33 (4)
Na1—O4—H4B	115 (2)	O4—Na1—Na1^i	96.58 (5)
H4A—O4—H4B	103 (2)	O5^i—Na1—Na1^i	44.01 (3)
Na1—O5—Na1^i	89.66 (5)	O1—As1—O2	112.39 (5)
Na1—O5—H5A	118.1 (16)	O1—As1—C2	109.94 (7)
Na1^i—O5—H5A	103.1 (16)	O2—As1—C2	108.19 (8)
Na1—O5—H5B	114.9 (15)	O1—As1—C1	107.96 (8)
Na1^i—O5—H5B	126.6 (17)	O2—As1—C1	108.77 (7)
H5A—O5—H5B	105 (2)	C2—As1—C1	109.56 (9)

Symmetry code: (i) −x+1/2, −y+3/2, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H3A···O1	0.75 (3)	2.104	2.842 (2)	168.65
O3—H3B···O1^ii	0.75 (3)	2.045	2.788 (2)	168.71
O4—H4A···O2^iii	0.78 (3)	2.059	2.835 (2)	171.69
O4—H4B···O2^iv	0.82 (3)	2.005	2.823 (2)	175.19
O5—H5A···O2^v	0.78 (2)	2.070	2.849 (2)	175.02
O5—H5B···O2^vi	0.76 (2)	2.061	2.810 (2)	169.77
O6—H6A···O1^iv	0.71 (2)	2.053	2.758 (2)	176.06
O6—H6B···O4^vii	0.84 (3)	2.101	2.939 (2)	173.91

Symmetry codes: (ii) −x, y, −z+1/2; (iii) x, −y+2, z+1/2; (iv) −x+1/2, y+1/2, −z+1/2; (v) −x+1/2, y−1/2, −z+1/2; (vi) x+1/2, −y+3/2, z+1/2; (vii) −x+1, −y+2, −z+1.